State of trust networks (Score 1)

What is the current state of trust networks? Many problems (spam, SEO, 'gaming') seem to hinge on the absence of a trust certificate for ratings. Further, the value of ratings is subjective. I shouldn't have to `trust' Wikia selected users with their ratings. I myself should choose users whose ratings I value for a particular topic.

Is there some fundamental flaw in current trust network algorithms that prevent them from being implemented?